The present invention relates to apparatus for admixing a foam-liquid solution with water in a predetermined proportion in a foam-water fire fighting system.
In foam-water fire fighting systems, the demand for the foam-liquid mixture can be expected to vary considerably depending upon the rate of application of the mixture. For example, it is not uncommon for the flow rate to vary from as low as 20 gpm to as high as 1000 gpm during fire fighting operations. In order to ensure satisfactory results, the foam should be mixed with water in a predetermined proportion, and the proportion should be relatively constant over the entire flow range. In order to maintain adequate pressure at the nozzle to ensure proper distribution of the mixture, the apparatus which admixes the foam with the water should create a minimum pressure drop in the supply line.
Another application requiring a very good turndown ratio, i.e., extremely accurate proportioning down to very low volumes, is the case of a sprinkler system for fighting fires in a warehouse or the like. In this application it is important to put an accurate percentage of additive, whether it is a foam type of liquid, a penetrating agent, or an ablative agent, into the fire fighting stream of water. Typically, the additive may consist of a 3% foam liquid. The main problem with a sprinkler facility is that it is unattended and it is not possible to know beforehand how much water is going to be required. Moreover, it is not known whether one sprinkler head is going to open or whether all of them are going to open and, in either case, it is necessary to be able to provide the right percentages of the water and additive.
Acknowledgement is made of the proportioning devices disclosed in U.S. Pat. Nos. 3,380,467; 3,647,002; and 4,064,891.
U.S. Pat. No. 3,380,467 discloses a proportioning apparatus particularly useful in the agricultural industry as a means for medicating the drinking water of livestock. The proportioning apparatus is usually mounted in the water feed line and serves to automatically and continuously mix predetermined quantities of a liquid additive, such as medication, to the drinking water delivered to the feed troughs for consumption by the livestock. The device consists of a diaphragm with a shuttle valve arranged so that the water from the water feed line enters on each side of the diaphragm to push the diaphragm back and forth. The diaphragm has a small piston pump to meter in the additive for the livestock drinking water. The device is constructed so that the faster the livestock drink the water, the faster the device operates to meter in more additive so that the livestock are provided with a constant amount of additive per gallon of water.
U.S. Pat. No. 3,647,002 discloses an apparatus used to admix a foam solution with water in a foam-water fire fighting system. The apparatus comprises a number of moving parts and is relatively complex in construction. Also, the patented valve structure is spring-loaded into a closed position whereby the water must act against increasing spring pressure and the water flow rate through the valve increases and this has the effect of increasing the pressure drop across the valve at higher flow rates and reducing pressure at the discharge nozzle. As a result, the effectiveness of distribution of the mixture may be significantly impaired.
U.S. Pat. No. 4,064,891 discloses apparatus for admixing a foam solution with water in a foam-water fire fighting system in a manner which accurately meters the amount of foam mixed with the water to ensure an optimum portion of foam to water over a wide range of flow rates of the foam-water mixture. The device of this patent uses a balanced pressure proportioning device and a float valve that floats on the stream. The float valve will sink in the water but it floats against the pressure drop and meters out the right amount of foam liquid, i.e., a certain fixed percentage of foam liquid. The device is constructed to put out a certain percentage of foam liquid additive regardless of how much water is coming through whereby if the float raises up to the top for high volume, then the restriction for the foam liquid opens up and lets a large amount of foam to go through. The device has a built in regulating valve which enables the maintaining of the approximate same pressure on the foam liquid side as you have on the water side. Accordingly, with the same pressure on the foam liquid as on the water, the metering valve is then sized to provide a very precise ratio. With this balanced pressure system there is provided an external foam pump usually driven by an electric motor which is triggered whenever there is some demand causing a pressure drop in the sprinkler system or in the fire hose or whatever.